In a higher-capacity hard disk drive (HDD), a track pitch becomes narrower and it becomes difficult to maintain a uniform track pitch and track pitch abnormality in which the track pitch becomes narrower than a reference track pitch might occur. The track pitch abnormality might have effects of (I) occurring close writing to an adjacent track and (II) adjacent track interference (ATI) on the HDD becomes large.
Measures against the close writing or measures against the ATI are based on a constant track pitch, and the track pitch abnormality is not taken into consideration. Therefore, the measures against the close writing or the measures against the adjacent track interference in which the track pitch abnormality is taken into consideration are required.